1. Technical Field
The present disclosure relates to a lifter structure.
2. Related Art
A lifter structure has conventionally been known which is used in a fuel pump pressurizing fuel fed from a fuel tank to supply pressurized fuel to an injector in vehicles, for example.
Japanese Patent Application Publication, JP-A-2009-236041, discloses a lifter structure including a cylinder, a plunger, a lifter guide and a lifter.
A lower end of the cylinder is connected via a spring seat to an upper end of the lifter guide. The cylinder is formed with a guide hole into which the plunger is inserted. The lifter guide also has a bore into which the lifter is inserted. The plunger has a lower end which faces the bore interior and is in abutment with the lifter. The lifter includes a lifter body, a pair of opposed walls continuous to a lower end of the lifter body, a roller disposed between the opposed walls, and a pin which extends through the roller, the opposed walls and has both ends swaged onto outer surfaces of the opposed walls respectively. The roller has an outer circumferential surface which is in abutment with a cam. Both lifter and plunger are biased to the cam side by a coil spring interposed between the lifer and the spring seat. A pump chamber is defined between an upper end of the plunger and the cylinder.
Upon rotation of the cam, the roller is rotated about the pin to drive the lifter upward. In this case, the lifter body is moved upward while sliding on an inner circumferential surface of the bore. With this, the plunger is also moved upward, whereupon the volume of the pump chamber is decreased (pressurization step). Upon further rotation of the cam, the lifter and the plunger are moved downward by the biasing force of the coil spring, whereupon the volume of the pump chamber is increased (suction step). The volume of the pump chamber is thus increased and decreased so that the fuel is sucked and discharged.
Both outer circumferential surface of the lifter body and inner circumferential surface of the bore have substantially truly circular sections respectively so that both surfaces are slidable on each other in the above-described conventional lifter structure. As a result, the lifter body is prevented from free motion (backlash) in the bore.
However, when both ends of the pin are swaged onto the outer surfaces of the opposed walls, an excessive swaging force is applied to the opposed walls. Accordingly, the walls sometimes fall down inward so as to come closer to each other. In this case, an adverse effect of deformation of the opposed walls reaches parts of the outer circumferential surface of the lifter body located at the same side as the opposed walls, whereupon the circularity of the outer circumferential surface of the lifter body cannot sometimes be maintained. More specifically, the lifter body includes first parts of the outer circumferential surface located at the same side as both opposed walls. Each first part of the lifter body will be referred to as “swaging side region.” The lifter body also includes other or second parts of the outer circumferential surface located at a side perpendicular to both opposed walls. Each second part will be referred to as “non-swaging side region.” In this case, the lifter body is sometimes plastically deformed so that the swaging side regions sometimes would bulge radially outward and so that the non-swaging side regions are degenerated radially inward.
Consequently, since an outer diameter of the lifter body between the swaging side regions exceeds an inner diameter of the bore, there is a possibility that the lifter body cannot be inserted into bore or that the lifter body may be forced into the bore. On the other hand, when an overall inner diameter of the bore is previously rendered larger in anticipation of deformation of the lifter body, a gap larger than an allowable one would be formed between the outer circumferential surface of the lifter body and the inner circumferential surface of the bore. The lifter body is would be rickety within the range of the gap, whereupon there is a possibility that a sliding friction may occur between the outer circumferential surface of the lifter body and the inner circumferential surface of the bore or abnormal noise may be produced.